Introduction

For home gardeners, raspberries are one of the easiest fruits to grow. Raspberries grown in Minnesota have relatively few insect pests and diseases. Gardeners who use Integrated Pest Management (IPM) practices often have good yields every year without applying pesticides. IPM is a sustainable approach that allows gardeners to reduce pests to a tolerable level by using the best balance of cultural, physical, biological, & chemical management strategies. IPM takes into account the level of damage a pest is capable of causing, as well as the possible risks to humans and the environment associated with each pest management strategy.

To properly diagnose pest problems on raspberry plants, it is important to understand the normal growth pattern of these plants. Raspberry plants consist of first year canes (primocanes) and second year canes (floricanes). In Minnesota, gardeners may grow summer-bearing raspberries or fall-bearing raspberries. Summer-bearing raspberries only produce fruit on floricanes, while fall-bearing raspberries produce fruit on primocanes as well as floricanes. Floricanes die after harvest in the middle of summer, while primocanes actively grow through August and have green bark until early September. When trying to identify what is killing leaves or canes, always check to see if the symptoms are on the primocanes or floricanes. Since floricanes die in the middle of summer, yellow and dying leaves on floricanes after June is considered normal, but yellow leaves on primocanes may indicate a problem.

Cultural controls can be very effective in protecting raspberries from most insect pests and diseases common in Minnesota. The first step is proper care of the plants. Information on the best way to care for raspberries is provided in the University of Minnesota Extension publication "Raspberries for the Home Garden". Cultural practices such as site selection, cane removal, variety selection and irrigation all contribute to developing a good, healthy raspberry stand. One key to effective IPM is to prevent diseases before they occur and to treat the pathogen or insect pest at susceptible life stages, before significant damage can occur. Many cultural control practices should be implemented before insect pests and disease become evident as they are largely preventative in nature.

In IPM, pesticide sprays are used only when cultural controls are not effective or as a supplement to cultural controls. If using pesticides, gardeners should choose an effective product that has the lowest impact on human health, non-target organisms like bees and the environment. Information on using pesticides safely for home gardeners can be found at the Pesticide Environmental Stewardship website or the National Pesticide Information Center website. Information on the correct way to apply specific pesticides can be found on the product label. If pesticides are necessary, always use them exactly as directed by the product label as mandated by federal law.

Preventing pests before and during the establishment year

Some of the worst pest problems in raspberries can be avoided or reduced with proper care before planting and during establishment. If possible, remove or kill any wild brambles, old raspberry plants, or weeds near the site of the new raspberries. Wild raspberries and weeds can act as a source of viral and fungal diseases that can harm your new plants as well as hosts for insect pests, thus providing a potential reservoir for pests in the area.

Obtain plants only from a reputable wholesale or a retail nursery, preferably one that sells certified virus-free planting stock. Raspberry plants can be bought as dormant crowns, or as potted plants from a retail nursery. Dormant crowns come as roots with a cane. Cut the cane back to five inches. About half of the time, the cane will not sprout, but multiple canes will sprout from the roots.

Choose a site with well-drained soil or amend the soil to improve drainage. Avoid sites that could have alkaline or clay soils. A soil test will tell you if the soil is deficient in any major nutrients or if the pH is too high or low. To reduce fungal diseases, the raspberries should also be in a place where breezes can dry the foliage off after a heavy rain or dew.

Weeds

Weeds can stunt raspberry plants and make raspberries more vulnerable to diseases by decreasing air movement in the patch and by acting as a source of pests or pathogens. Perennial weeds should be controlled before planting, and annual weeds should be controlled during the first year. Once raspberries are well established, raspberry plants crowd out most annual weeds.

Kill perennial weeds in the site where the raspberries will be the summer before planting. The two worst perennial weeds in Minnesota raspberries are quackgrass and Canada thistle. When possible, choose a site without any Canada thistles. Canada thistle is most susceptible to herbicides just before it blooms in late June, but stays susceptible to herbicide until the middle of October. Quackgrass is most susceptible to herbicides in late fall. Both quackgrass and thistles are hard to kill by hoeing and pulling due to their extensive root systems. Both weeds will choke out young raspberry plants if the weeds are not removed prior to planting.

Annual weeds need to be controlled after planting. Avoid using herbicides during the planting year as most herbicides have the potential to harm the plants. The most effective way to control weed seedlings is with a combination of hand weeding and mulch. Shallow hoeing around the plants is necessary to kill weed seedlings. By the middle of summer, healthy plants will start sending out rootsuckers that can sprout and become new canes away from the mother plants. Since hoeing can damage new canes, many growers apply straw mulch in July. The straw mulch prevents most annual weeds from sprouting. New canes will usually be able to sprout through the straw mulch.

Forming the raspberry row

Always grow raspberries in a row. Left uncontrolled, raspberries will grow into a large, round, impenetrable patch. Confining raspberries to a row that is two feet wide or less will cut down on the most common fungal diseases, such as the fruit disease gray mold or the cane disease spur blight. Red raspberries spread underground through rootsuckers, with roots extending ten or more feet from the original mother plant in just one year. Black raspberries primarily spread through tip rooting, which occurs when the tip of a new cane touches the soil and starts forming roots. All raspberries have the potential to spread into ornamental perennial beds, tilled vegetable gardens and shrub gardens, including blueberry patches. Placing sod between the raspberries and the garden will keep raspberries in a row while keeping them out of other desirable plants.